In practice, hydraulically-driven tools such as joining tools are widespread. They consist for example of a setting punch that is driven by a hydraulic cylinder and is connected with the assistance of hoses to a remotely located hydraulic source. In addition to the required space for the hydraulic source, the long hydraulic hoses are responsible for poor efficiency, undesirable interruptions or impairments during the process.
To avoid the involved equipment in terms of hydraulic hoses and the hydraulic source, increasingly, operating modules are desired that form a single operating unit. These single operating modules are driven electrically or electrohydraulically as for example described in DE 10 2014 200 962 A1 and in DE 11 2005 002 804 B4.
DE 10 2014 200 962 A1 uses two coaxially-arranged spindles that are offset in a straight line with the assistance of an electric motor. A differential gear unit transmits the movement of the electric motor specifically to one or the other spindle. The differential gear unit converts the movement of the electric motor such that the first spindle, and accordingly the punch, are moved in a movement step quickly and with minimal force to the joining site. The punch is moved in a power step by the second spindle and the switched differential gear unit. This means that greater force can be applied by the punch than in the movement step. To accomplish this, the punch can only travel a shorter path per unit time than in the movement step. It is also disclosed to move the two spindles alternatively with different drives.
The single operating hydraulic unit of DE 11 2005 002 804 B4 combines two hydraulic pumps, a hydraulic reservoir, and a valve block. Depending on the respective application, these generate a low-pressure or high-pressure partial flow of the hydraulic fluid for operating a connected hydraulic cylinder of a blind rivet setting tool. The low-pressure partial flow provides a high volumetric flow with low power capacity so that the punch can be quickly moved over long punch paths. The high-pressure partial flow provides a low volumetric flow with high power capacity so that, in comparison to the low-pressure partial flow, high punch forces can be realized over short punch paths.
The single operating drive units that work in multiple steps cannot be operated efficiently with the existing equipment. A disadvantage is revealed especially when switching between the movement step, for example the step with the hydraulic low-pressure partial flow and the power step, such as the step with the hydraulic high-pressure partial flow. Since the switchover point is not precisely defined, both early and late switching from the movement step to the power step causes an uneconomical delay in the joining process. If the switching is too early, a punch path that is still pending is only traveled with a low punch speed. This delays the joining process. If the switch to the power step is too late, the punch attempts to join the components without being able to apply the required force. This also leads to an undesirable delay in the joining process.
An object of at least some embodiments of the present invention is therefore to provide a joining device and a joining method by means of which the known joining processes can be controlled and hence performed more effectively.